Multilayer ceramic circuit boards are made from layers of green ceramic tapes. A green tape is made from particular glass compositions and optional ceramic powders which are mixed with organic binders and a solvent, cast and cut to form the tape. Wiring patterns can be screen printed onto the tape layers to carry out various functions. Vias are then punched in the tape and are filled with a conductor ink to connect the wiring on one green tape to wiring on another green tape. The tapes are then aligned, laminated, and fired to remove the organic materials, to sinter the metal patterns and to crystallize the glasses. This is generally carried out at temperatures below about 1000° C., and preferably from about 750–950° C. The composition of the glasses determines the coefficient of thermal expansion, the dielectric constant and the compatibility of the multilayer ceramic circuit boards to various electronic components.
More recently, metal support substrates (metal boards) have been used to support the green tapes. The metal boards lend strength to the glass layers. Moreover since the green tape layers can be mounted on both sides of a metal board and can be adhered to a metal board with suitable bonding glasses, the metal boards permit increased complexity and density of circuits and devices. In addition, passive and active components, such as resistors, inductors, capacitors and the like, can be incorporated into the circuit boards for additional functionality. Thus this system, known as low temperature cofired ceramic-metal support boards, or LTCC-M, has proven to be a means for high integration of various devices and circuitry in a single package. The system can be tailored to be compatible with devices including silicon-based devices, indium phosphide-based devices and gallium arsenide-based devices, for example, by proper choice of the metal for the support board and of the glasses in the green tapes.
The ceramic layers of an LTCC-M structure must be matched to the thermal coefficient of expansion of the metal support board. Glass ceramic compositions are known that match the thermal expansion properties of various metal or metal matrix composites. These compositions are disclosed for example in U.S. Pat. No. 5,625,808 to Tormey et al; U.S. Pat. No. 6,017,642 to Kumar et al; U.S. Pat. No. 5,256,469 to Cherukuri et al; and U.S. Pat. No. 5,565,262 to Azzaro et al. U.S. Pat. No. 5,581,876 to Prabhu et al. disclose bonding glass compositions for adhering ceramic layers to metal support substrates. These composition patents are incorporated herein by reference.
While conventional LTCC and LTCC-M boards provide superior temperature control and heat dissipation adequate for most common circuit components, they may not offer sufficient power dissipation for all forms of high power components such as high power resistors. For example, the boards do not permit the printing of typical high power resistors on the board surface. Rather, they require the use of surface mount chip power resistors at greater expense and complexity of fabrication. Accordingly, it would be desirable to provide a method and structure for enhanced temperature control of multilayer LTCC and LTCC-M boards.